This figure shows the history of atmospheric carbon dioxide concentrations as directly measured at Mauna Loa, Hawaii. This curve is known as the Keeling curve, and is an essential piece of evidence of the man-made increases in greenhouse gases that are believed to be the cause of global warming.

Photograph by Narayanese and Semhur, courtesy Wikimedia, and the NOAA Mauna Loa Observatory

Download this file

  • On June 13, 2002, American chemist Charles Keeling was awarded the National Medal of Science by President George W. Bush. Keeling had spent years documenting increasing concentrations of carbon dioxide in the atmosphere—the Keeling curve. Keeling tracked the curve by taking precise measurements from an observatory atop Mauna Loa, a volcano in Hawaii. The data were initially collected between 1958 and 1960 and measurements are still taken today.


    Keeling also calculated the amount of carbon dioxide created from burning fossil fuels each year, and noticed a correlation between that calculation and the Keeling curve. This was one of the first indications to scientists that human activity could have a major effect on Earth's climate.

  • Term Part of Speech Definition Encyclopedic Entry
    carbon dioxide Noun

    greenhouse gas produced by animals during respiration and used by plants during photosynthesis. Carbon dioxide is also the byproduct of burning fossil fuels.

    Charles Keeling Noun

    (1928-2005) American scientist who confirmed the accumulation of CO2 in the atmosphere 

    chemist Noun

    person who studies the theory and application of atoms and molecules, and their relationships and interactions.

    climate Noun

    all weather conditions for a given location over a period of time.

    Encyclopedic Entry: climate
    data Plural Noun

    (singular: datum) information collected during a scientific study.

    fossil fuel Noun

    coal, oil, or natural gas. Fossil fuels formed from the remains of ancient plants and animals.

    initially Adverb

    at first.

    Keeling curve Adjective
    precise Adjective


    volcano Noun

    an opening in the Earth's crust, through which lava, ash, and gases erupt, and also the cone built by eruptions.

    Encyclopedic Entry: volcano